Coccoloba-associated xerocomoid boletes (Boletaceae) from the Caribbean and Mexico: Tropicoboletus ruborculus gen. et comb. nov., revision of Xerocomus coccolobae, phylogenetic assessment of Singerocomus guadelupae comb. nov., and type studies of Xerocomus caeruleonigrescens, X. cuneipes, and X. pseudoboletinus var. pini-caribaeae

Abstract

Abstract Only two Coccoloba-associated xerocomoid boletes with smooth basidiospores are currently known from the Dominican Republic, namely Boletus ruborculus and Xerocomus coccolobae. A multilocus phylogenetic analysis of four gene markers (ITS, LSU, RPB2, TEF1) reveals that B. ruborculus forms an autonomous clade in the Boletaceae corresponding to a novel genus, which is introduced here as Tropicoboletus gen. nov., whereas X. coccolobae is confirmed as a member of Xerocomus s. str. Tropicoboletus is sister to subfamily Xerocomoideae in the combined RPB2/TEF1 Boletaceae-wide analysis. Accurate morphological descriptions of the two species based on well-annotated samples are provided, accompanied by color photographs of fresh specimens in habitat and line drawings of their main anatomical features. The holotype collections of B. ruborculus and X. coccolobae were successfully sequenced and re-examined anatomically. The distribution range of Tropicoboletus ruborculus comb. nov. is extended from the original locality in Puerto Rico to the Dominican Republic and Mexico where its presence is reported for the first time. Similarly, the Dominican collections of X. coccolobae represent the first documented occurrence of this species for the Island of Hispaniola. Based on molecular and morphological evidence, we conclude that the Belizean species Xerocomus olivaceus is conspecific with X. coccolobae and is therefore reduced into synonymy. In addition, the holotypes of Xerocomus caeruleonigrescens, Xerocomus cuneipes, and Xerocomus pseudoboletinus var. pini-caribaeae were microscopically re-studied, although their exact taxonomic placement remains unresolved in the absence of any phylogenetic inference. Molecular investigation of a paratype of Boletus guadelupae resulted in a conspecificity with the recently described Singerocomus atlanticus from Brazil, extending the biogeographic coverage of Singerocomus to the Caribbean. Accordingly, the new combination Singerocomus guadelupae is proposed and S. atlanticus is synonymized. Finally, a putative novel Xerocomus s. str. species is discovered from the Dominican Republic but not formally described for the time being due to the paucity of material available.